Athletes run anti-clockwise so that their right leg – for most people the stronger – runs the greater distance.

another writer suggested that it is due to the position of the heart:

When I was a junior athlete I asked the same question of a leading coach and sports doctor. They both told me that it was all to do with the position of the heart, which sits on the left side of the chest. This makes running anti-clockwise more natural and comfortable.

Is running anti-clockwise easier than running clockwise, and if so why?

+1 - I think it is because when they started doing races time was going backward. When time started going forwards and the clocks changed the runners were used to going that direction so it is a legacy from when time ran backwards. - Cliff Claven successfully channeled :)
– ChadJul 13 '12 at 13:26

5

@Chad - In a vain attempt to channel Woody, I thought it was because runners as a group tend to be democrats, so they naturally lean to the left.
– user3344Jul 13 '12 at 14:18

Of course this is true, but only true for those born in the northern hemisphere. Those who were born in the southern hemisphere will run best on tracks that wrap in the opposite direction. It also explains why there are not many good track runners who were born in Antarctica, more clearly confirming evidence. They would be able to run well only on highly curved clockwise tracks. Finally, this hypothesis explains why the best marathoners in the world were all born near the equator, as they can run best in a straight line. All is clear to me now. :)
– user3344Sep 18 '12 at 13:50

1

It would be interesting to see the statistics from racehorses - do they prefer racetracks in one direction? Confounding variables might make it hard to draw a conclusion though.
– Oddthinking♦Dec 9 '12 at 22:39

In this study, they led blindfolded people attempt to walk straight in a room without any clues. They found that, for the total number of trials, 50% trajectories terminated on the left side, 39% on the right side and 11% were defined as “straight”. Quoting from the article:

Results were considered statistically significant for P<0.05. (...) One striking characteristic is the wide variability of the trajectories; some of them reached the edge of the area (Y axis) in less than 30 m (in the X direction) while other trajectories still remained straight at 140 m. The majority (50%) of the trajectories ended on the left side, 39% on the right side and 11% were defined as “straight”

This result shows that statistically speaking, on average, people do tend to turn left more easily than right, although the variability is large. This may suggest that running in a left-hand turn (counter-clockwise) is easier than in a right-hand turn (clockwise), because the left-hand turn would — statistically speaking — be the most likely to happen among the three alternatives left, straight, or right.

As to the why, this may not be strictly on-topic on Skeptics.SE, but quoting from the abstract (emphasis mine):

Posturographic analysis, used to assess if there was a relationship between functional postural asymmetry and veering revealed that the mean position of the center of foot pressure during balance tests was correlated with the turning score. Finally, we established that the mean position of the center of pressure was correlated with perceived verticality assessed by a subjective verticality test. Together, our results suggest that veering is related to a “sense of straight ahead” that could be shaped by vestibular inputs.

So, if we believe this article, neither of the reasons you quoted is correct.

Thanks go to my secondary school Biology teacher for his claim (some time around 2002) that when people cross over a field of grass in a park (e.g. to cut off a corner), the resulting path is not straight, but slightly curved, as can be easily seen by looking at the trail; he said that this was due to the asymmetry of the human body. I found the above article by his merit.

The study doesn't show that it's "easier" to turn left, but that people tend to naturally move to the left, which "could be shaped by vestibular inputs", where vestibular means "relating to a vestibule, particularly that of the inner ear, or more generally to the sense of balance", which doesn't neccessarily mean it's easier, just a more natural tendency when the subject has no visual reference, which is not the case when running.
– JohnnyMay 16 '17 at 21:59

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